The invention relates to a device for the high-speed conveying of flat objects, comprising a fixed sole plate extending along the path which the conveyed flat objects follow and along which the flat objects, standing on edge and arranged in series, glide, a motorized endless reference belt stretched along one side of the sole plate, a motorized endless press belt stretched along the other side of the sole plate, and means for elastically pressing the press belt against the reference belt in such a way as to grip the flat objects arranged on the sole plate between the reference belt and the press belt. The invention relates more specifically to a unit for conveying post envelopes in series edge-on between a destacking unit and a sorting unit of a machine for processing mail.
Postal processing machines have to be designed to be able to accept a broad range of postal items. More specifically, they have to be designed to take flat rectangular envelopes the thickness of which varies between 0.15 and 32 millimeters whereas the length and width of these envelopes can vary respectively between 14 and 40 centimeters and between 9 and 30 centimeters. Hitherto, in units for conveying post envelopes in series edge-on, the motorized reference belt has been a fixed backing belt, conventionally mounted on a collection of pulleys of stationary vertical spindle, and the press belt has been pressed against the reference belt by pulleys with a mobile rotation spindle, mounted on arms which have been returned elastically by springs. As the envelopes in series edge-on between the two belts, namely the reference belt and the press belt, are moved along by friction, it is essential that the press belt be pressed firmly against the reference belt on each side of each envelope regardless of its thickness so as to guarantee that the envelopes will be moved along at uniform speed maintaining a constant spacing between consecutive envelopes from the entry to the exit of the conveying unit. As two consecutive envelopes moved along in the conveying unit at a speed in excess of 3 meters per second may have thicknesses which vary between 0.15 and 32 millimeters, it is essential that the means used to keep the press belt pressed against the reference belt have positional-return dynamics designed accordingly. Now, it has become apparent that the spring-retum of a pulley customarily used to press the press belt against the reference belt is unable to obtain optimum positional-retum of the pulley for all extreme variations in thickness of post envelopes. It then follows that the post envelopes arranged in series in the conveying unit have a speed of travel that fluctuates and results in variations in the spacing between consecutive envelopes in the conveying unit. This variation in the spacing between consecutive envelopes leads to disruptions at the character-recognition-address processing unit which may be installed on the path followed by the conveyed post envelopes. Finally, the rotary arms on which the pulleys are mounted require constant and expensive maintenance because it is essential to anticipate their seizure in order to prevent blockages at the exit from the conveying unit.
The object of the invention is therefore to overcome the aforementioned drawbacks of the state of the art and the invention therefore relates to a device for the high-speed conveying of flat objects, particularly post envelopes, comprising a fixed sole plate extending along the path which the conveyed flat objects follow and along which the flat objects, standing on edge and arranged in series, glide, a motorized endless reference belt stretched along one side of the sole plate, a motorized endless press belt stretched along the other side of the sole plate, and means for elastically pressing the press belt against the reference belt in such a way as to grip the flat objects arranged on the sole plate between the reference belt and the press belt, wherein said means consist of a series of elastomer wheels aligned along said other side of the sole plate, each wheel having a hub mounted to rotate on a stationary spindle, and an annular tread strip in contact with the press belt, the hub and the annular tread strip of each wheel being connected by elastically deformable circular-arc-shaped fins, the two ends of each fin, which are for connection to the hub and to the annular tread strip of the wheel, lying on a radius of the wheel.
Each elastomer wheel with elastically deformable fins is a large-diameter wheel allowing sufficient deformation to absorb the variations in thickness up to 40 millimeters with an appreciably constant compression force. The special profile of the fins, in the shape of arcs of a circle, with points of attachment located on the radius of the wheel, allows the elastomer to work along the entire length of the fins when the wheel is compressed without creating any stress-concentration zones, thus contributing to extending the life of the wheel.